1. Field of the Invention
This invention relates to a method for testing the condition of well bore formations for cementing a production casing to the wall of the well bore and more particularly to a method for indicating the flow of fluid into or out of the formations surrounding the well bore and the emission of gas from the surrounding formations into the well bore.
2. Description of the Prior Art
In conventional drilling operations in prospecting for minerals of a gaseous or liquid nature, well bores are drilled. After the well bore has been drilled and the decision made to complete the well for production of the desired mineral, a production casing for subsequent completion and production procedures is installed. It is conventional practice to secure the production casing in the well bore by means of cement.
The cementing operation is carried out by pumping a cement slurry down the inside of the production casing to the bottom of the casing and therefrom up around the casing into the annulus between the casing and the wall of the well bore. In this manner the production casing is cemented in the well bore along all or selected portions of the length of the production casing. For subsequent completion and production operations, it is important that a good bond exist between the production casing and the cement, as well as between the cement and the formations comprising the wall of the well bore after the cement has set. However, problems are encountered in obtaining the required bond when the cement slurry and/or other fluids used in the cementing procedure are lost from the annulus between the production casing and the wall of the well bore by the flow thereof into permeable formations, or fractures, cavities or fissures in formations surrounding the well bore. This loss or in certain instances, flow of fluid from formations into the well bore usually results in a poor cement job, as for example, incomplete cementing, movement and weakening of setting cement, unsatisfactory cement bond to the casing and/or formations in the well bore. In addition, the cementing of the production casing is adversely affected by the emission of gas from the well bore formations causing voids or channels in the cement, unsatisfactory bond and unstable conditions in and above the setting cement. It is essential, therefore, that the condition of the well bore formations be known by testing before cementing the production casing so that remedial action can be taken if adverse conditions exist.
Though monitoring during drilling operations for a loss of drilling fluid to the well bore formation or the intrusion of formation fluid into the well bore is disclosed by U.S. Pat. No. 3,857,281, the method and operation disclosed relates to maintaining the requisite volume of drilling fluid within the well bore to insure that a dangerous condition, such as a blowout condition, does not arise during times when the drill string is either being run into or removed from the well bore. This method and apparatus does not indicate the condition of the well bore formations as to the emission of gas from the well bore formations or concern itself with borehole conditions in the installation of production casing.
A system for automatically filling well bores with drilling fluid during drilling operations is disclosed in U.S. Pat. No. 3,833,076. There a volume of drilling fluid entering the well bore is continually monitored. The apparatus is operable to signal a loss of the drilling fluid in excess of a predetermined threshold. The problem of maintaining fluid level in the well bore becomes particularly acute when the drill string is withdrawn from the hole and there is a lowering of the fluid level within the hole caused by the absence of the drill string body which when removed displaces a considerable amount of fluid. Also, it is noted that the fluid level in the well bore may be lowered by filtration of a portion of the liquid into the porous formations surrounding the well bore. However, the above system is confined to maintaining the drilling fluid level within a well bore and automatically pumping into the well bore the amount necessary to maintain a predetermined amount of drilling mud therein.
Similarly, U.S. Pat. No. 3,614,761 discloses a method and apparatus for monitoring potential blowouts or lost circulation in a well. The apparatus monitors for potential blowouts by sensing devices on the drilling fluid pump and the well bore return pipe to the drilling fluid pit. A signal is generated indicating flow of the drilling fluid out of the well bore. U.S. Pat. No. 3,638,485 discloses monitoring the drilling fluid level to warn of an intrusion of formation fluids. U.S. Pat. No. 2,966,059 discloses fluid monitoring means in a drilling mud system to indicate gain or loss of fluid to or from the formation. U.S. Pat. Nos. 3,550,445, 3,602,322 and 3,726,136 disclose monitoring and control apparatus for maintaining a preselected volume of drilling fluid in the well bore.
While it has been suggested to monitor the drilling fluid level in a well bore to assure that blowout conditions do not occur, the prior art systems are not directed to testing, the condition of well bore formations, the loss of fluid into or flow from the formations surrounding the well bore and the emission of gas from the formations surrounding the well bore in preparation for cementing production casing in the well bore. Much of present day drilling is performed with drilling fluids which do not condition the well bore, well bore wall or formations surrounding the well bore properly for successful cementing of production casing. In addition, much of present day drilling is performed with air or gas as a drilling medium making impossible the determination of the condition of the well bore formations relative to the behavior of the liquids which will be used in cementing the production casing. Therefore, there is a need to provide method and apparatus for determining that the condition of the well bore formations is satisfactory in preparing the well bore for cementing the production casing in the well bore, particularly when such determination has been impossible or inconclusive prior to running the production casing into the well bore.